This invention relates to the production of the commercially useful hydrated iron oxide pigment, which is yellow in color and is known, and will hereinafter be referred to as yellow iron oxide pigment.
Yellow iron oxide pigment has been made by treating a soluble ferrous salt with an alkali metal carbonate or hydroxide, in the presence of oxygen, so as to precipitate the required yellow iron oxide pigment. In practice an overdose of alkali metal carbonate or hydroxide will result in a commercially valueless rust coloured hydrated iron oxide being produced by this process.